Abemaciclib plus trastuzumab with or without fulvestrant versus trastuzumab plus standard-of-care chemotherapy in women with hormone receptor-positive, HER2-positive advanced breast cancer (monarcHER): a randomised, open-label, phase 2 trial

Mechanisms of sensitivity and resistance to CDK4/CDK6 inhibitors in hormone receptor-positive breast cancer treatment

Cell cycle dysregulation is a hallmark of cancer that promotes eccessive cell division. Cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6) are key molecules in the G1-to-S phase cell cycle transition and are crucial for the onset, survival, and progression of breast cancer (BC). Small-molecule CDK4/CDK6 inhibitors (CDK4/6i) block phosphorylation of tumor suppressor Rb and thus restrain susceptible BC cells in G1 phase. Three CDK4/6i are approved for the first-line treatment of patients with advanced/metastatic hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) BC in combination with endocrine therapy (ET). Though this has improved the clinical outcomes for survival of BC patients, there is no established standard next-line treatment to tackle drug resistance. Recent studies suggest that CDK4/6i can modulate other distinct effects in both BC and breast stromal compartments, which may provide new insights into aspects of their clinical activity. This review describes the biochemistry of the CDK4/6-Rb-E2F pathway in HR+ BC, then discusses how CDK4/6i can trigger other effects in BC/breast stromal compartments, and finally outlines the mechanisms of CDK4/6i resistance that have emerged in recent preclinical studies and clinical cohorts, emphasizing the impact of these findings on novel therapeutic opportunities in BC.

Recent progress of CDK4/6 inhibitors' current practice in breast cancer

Dysregulated cellular proliferation represents a hallmark feature across all cancers. Aberrant activation of the cyclin-dependent kinase 4 and 6 (CDK4/6) pathway, independent of mitogenic signaling, engenders uncontrolled breast cancer cell proliferation. Consequently, the advent of CDK4/6 inhibition has constituted a pivotal milestone in the realm of targeted breast cancer therapy. The combination of CDK4/6 inhibitors (CDK4/6i) with endocrine therapy (ET) has emerged as the foremost therapeutic modality for patients afflicted with hormone receptor-positive (HR + )/HER2-negative (HER2-) advanced breast cancer. At present, the Food and Drug Administration (FDA) has sanctioned various CDK4/6i for employment as the primary treatment regimen in HR + /HER2- breast cancer. This therapeutic approach has demonstrated a substantial extension of progression-free survival (PFS), often amounting to several months, when administered alongside endocrine therapy. Within this comprehensive review, we systematically evaluate the utilization strategies of CDK4/6i across various subpopulations of breast cancer and explore potential therapeutic avenues following disease progression during application of CDK4/6i therapy.

Assessment of Treatment Sequence in Patients With Stage III Breast Cancer

INTRODUCTION

Stage III breast cancer is defined as locally advanced breast cancer and is treated with curative intent. Historically, overall survival (OS) did not differ based on treatment sequence (neoadjuvant chemotherapy [NAC] followed by surgery versus surgery followed by chemotherapy). Given recent advancements, we examined if treatment sequence may be associated with improved OS in a contemporary cohort of patients with stage III breast cancer.

METHODS

Patients aged 18-80 years with prognostic stage III breast cancer who received chemotherapy and surgery were selected from the Surveillance, Epidemiology, and End Results database. Patients were stratified by treatment sequence (NAC versus surgery first). Unadjusted OS and breast cancer-specific survival (BCSS) were estimated using the Kaplan-Meier method and compared with log-rank tests. Cox proportional hazards models were used to estimate the association of treatment sequence with OS and BCSS after adjustment for selected covariates.

RESULTS

The study included 26,573 patients; median follow-up was 62.0 months (95% confidence interval [CI] 61.0-63.0). Patients receiving NAC had a worse OS and BCSS compared to those who underwent surgery first (5-year OS rates 0.66 versus 0.73; 5-year BCSS rates 0.70 versus 0.77; both log-rank P < 0.001). After adjustment for tumor subtype, receipt of NAC (versus surgery first) remained associated with a worse OS (hazard ratio 1.27, 95% CI 1.2-1.34, P < 0.001) and BCSS (hazard ratio 1.35, 95% CI 1.27-1.43, P < 0.001).

CONCLUSIONS

Based on data from patients treated largely before 2020, undergoing surgery first may be associated with improved survival, even after adjustment for known covariates including tumor subtype. These findings may inform treatment when caring for patients with operable, locally advanced breast cancer.

The radiologist's role in detecting systemic anticancer therapy-related interstitial lung disease: an educational review

Systemic anticancer therapies (SACTs) are the leading cause of drug-induced interstitial lung disease (ILD). As more novel SACTs become approved, the incidence of this potentially life-threatening adverse event (AE) may increase. Early detection of SACT-related ILD allows for prompt implementation of drug-specific management recommendations, improving the likelihood of AE resolution and, in some instances, widening the patient's eligibility for future cancer treatment options. ILD requires a diagnosis of exclusion through collaboration with the patient's multidisciplinary team to rule out other possible etiologies of new or worsening respiratory signs and symptoms. At Grade 1, ILD is asymptomatic, and thus the radiologist is key to detecting the AE prior to the disease severity worsening. Planned computed tomography scans should be reviewed for the presence of ILD in addition to being assessed for tumor response to treatment, and when ILD is suspected, a high-resolution computed tomography (HRCT) scan should be requested immediately. An HRCT scan, with < 2-mm slice thickness, is the most appropriate method for detecting ILD. Multiple patterns of ILD exist, which can impact patient prognosis. The four main patterns include acute interstitial pneumonia / acute respiratory distress syndrome, organizing pneumonia, hypersensitivity pneumonitis, and non-specific interstitial pneumonia; their distinct radiological features, along with rarer patterns, are discussed here. Furthermore, HRCT is essential for following the course of ILD and might help to determine the intensity of AE management and the appropriateness of re-challenging with SACT, where indicated by drug-specific prescribing information. ILD events should be monitored closely until complete resolution. CRITICAL RELEVANCE STATEMENT: The incidence of potentially treatment-limiting and life-threatening systemic anticancer therapy-related interstitial lung disease (SACT-related ILD) events is likely increasing as more novel regimens become approved. This review provides best-practice recommendations for the early detection of SACT-related ILD by radiologists. KEY POINTS: Radiologists are crucial in detecting asymptomatic (Grade 1) ILD before severity/prognosis worsens. High-resolution computed tomography is the most appropriate method for detecting ILD. Drug-induced ILD is a diagnosis of exclusion, involving a multidisciplinary team. Familiarity with common HRCT patterns, described here, is key for prompt detection. Physicians should highlight systemic anticancer therapies (SACTs) with a known risk for interstitial lung diseases (ILD) on scan requisitions.

Depicting Biomarkers for HER2-Inhibitor Resistance: Implication for Therapy in HER2-Positive Breast Cancer

HER2 (human epidermal growth factor receptor 2) is highly expressed in a variety of cancers, including breast, lung, gastric, and pancreatic cancers. Its amplification is linked to poor clinical outcomes. At the genetic level, HER2 is encoded by the ERBB2 gene (v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 2), which is frequently mutated or amplified in cancers, thus spurring extensive research into HER2 modulation and inhibition as viable anti-cancer strategies. An impressive body of FDA-approved drugs, including anti-HER2 monoclonal antibodies (mAbs), antibody-drug conjugates (ADCs), and HER2-tyrosine kinase inhibitors (TKIs), have demonstrated success in enhancing overall survival (OS) and disease progression-free survival (PFS). Yet, drug resistance remains a persistent challenge and raises the risks of metastatic potential and tumor relapse. Research into alternative therapeutic options for HER2+ breast cancer therefore proves critical for adapting to this ever-evolving landscape. This review highlights current HER2-targeted therapies, discusses predictive biomarkers for drug resistance, and introduces promising emergent therapies-especially combination therapies-that are aimed at overcoming drug resistance in the context of HER2+ breast cancer.

The evolving landscape of metastatic HER2-positive, hormone receptor-positive Breast Cancer

Therapeutic agents targeting Human Epidermal Growth Factor Receptor 2 (HER2) demonstrated to positively impact the prognosis of HER2-positive breast cancer. HER2-positive breast cancer can present either as hormone receptor-negative or positive, defining Triple-positive breast cancer (TPBC). TPBC demonstrate unique gene expression profiles, showing reduced HER2-driven gene expression, as recapitulated by a higher proportion of Luminal-type intrinsic subtypes. The different molecular landscape of TPBC dictates distinctive clinical features, including reduced chemotherapy sensitivity, different patterns of recurrence, and better overall prognosis. Cross-talk between HER2 and hormone receptor signaling seems to be critical to determine resistance to HER2-directed agents. Accordingly, superior outcomes have been achieved with the use of endocrine therapy, representing the first subtype-specific pharmacological intervention unique to this subgroup. Additional targeted agents capable to tackle resistance mechanisms to anti-HER2, hormone agents, or both might further improve the efficacy of treatments, such as PI3K/AKT/mTOR inhibitors, particularly in a biomarker-enriched setting, and CDK4/6-inhibitors, with preliminary data suggesting a role of PAM50 subtyping to predict higher benefits in luminal tumors. Finally, the distinct biology of triple-positive tumors may yield the rationale for considering combinations within antibody-drug conjugate regimens. Accordingly, in this review, we summarized the current evidence and rationale for considering TPBC as a different entity, in which distinct therapeutical approaches leveraging on the different biological profile of TPBC may result in superior anticancer regimens and improved patient-centric outcomes.

Emerging treatments in HER2-positive advanced breast cancer: Keep raising the bar

Patients with human epidermal receptor 2 (HER2)-positive breast cancer are experiencing a consistent shift toward better survival across the years, thanks to tremendous advancements in treatment strategies. The consistent improvements of outcomes set a high bar for new drug development and the need to explore new ways to overcome resistance mechanisms. Emerging treatments in HER2-positive breast cancer aim to tackle the disease by acting on different targets, including not only HER2 (both at the extra- and intracellular level), but also HER3, PD-(L)1, CTLA4, NKG2A, AKT, PI3K, and, in triple-positive tumors, the estrogen receptors and the cyclin-dependent kinases 4/6. This review describes the evolving treatment landscape of HER2-positive breast cancer, from the current approved therapies to the future perspectives, with a focus on the new agents which are likely to get approved in the next future.

Molecular docking and MD simulation studies of 4-thiazol-N-(pyridin-2-yl)pyrimidin-2-amine derivatives as novel inhibitors targeted to CDK2/4/6

PURPOSE

Nowadays, cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have been approved for treating metastatic breast cancer and have achieved inspiring curative effects. But some discoveries have indicated that CDK 4/6 are not the requisite factors in some cell types because CDK2 partly compensates for the inhibition of CDK4/6. Thus, it is urgent to design CDK2/4/6 inhibitors for significantly enhancing their potency. This study aims to explore the mechanism of the binding of CDK2/4/6 kinases and their inhibitors to design novel CDK2/4/6 inhibitors for significantly enhancing their potency in different kinds of cancers.

MATERIALS AND METHODS

A series of 72 disparately functionalized 4-substituted N-phenylpyrimidin-2-amine derivatives exhibiting potent inhibitor activities against CDK2, CDK4 and CDK6 were collected to apply to this research. The total set of these derivatives was divided into a training set (54 compounds) and a test set (18 compounds). The derivatives were constructed through the sketch molecule module in SYBYL 6.9 software. A Powell gradient algorithm and Tripos force field were used to calculate the minimal structural energy and the minimized structure was used as the initial conformation for molecular docking. By the means of 3D-QSAR models, partial least squares (PLS) analysis, molecular dynamics (MD) simulations and binding free energy calculations, we can find the relationship between structure and biological activity.

RESULTS

In this study, we used molecular docking, 3D-QSAR and molecular dynamics simulation methods to comprehensively analyze the interaction and structure-activity relationships of 72 new CDK2/4/6 inhibitors. We used detailed statistical data to reasonably verify the constructed 3D-QSAR models for three receptors (q2 of CDK2 = 0.714, R2pred = 0.764, q2 = 0.815; R2pred of CDK4 = 0.681, q2 = 0.757; R2pred of CDK6 = 0.674). MD simulations and decomposition energy analysis validated the reasonability of the docking results and identified polar interactions as crucial factors that influence the different bioactivities of the studied inhibitors of CDK2/4/6 receptors, especially the electrostatic interactions of Lys33/35/43 and Asp145/158/163. The nonpolar interaction with Ile10/12/19 was also critical for the differing potencies of the CDK2/4/6 inhibitors. We concluded that the following probably enhanced the bioactivity against CDK2/4/6 kinases: (1) electronegative groups at the N1-position and electropositive and moderate-sized groups at ring E; (2) electrogroups featured at R2; (3) carbon atoms at the X-position or ring C replaced by a benzene ring; and (4) an electrogroup as R4.

CONCLUSION

Previous studies, to our knowledge, only utilized a single approach of 3D-QSAR and did not integrate this method with other sophisticated techniques such as molecular dynamics simulations to discover new potential inhibitors of CDK2, CDK4, or CDK6. So we applied the intergenerational technology, such as 3D-QSAR technology, molecular docking simulation techniques, molecular dynamics simulations and MMPBSA19/MMGBSA20-binding free energy calculations to statistically explore the correlations between the structure with biological activities. The constructed 3D-QSAR models of the three receptors were reasonable and confirmed by the excellent statistical data. We hope the results obtained from this work will provide some useful references for the development of novel CDK2/4/6 inhibitors.

heredERA Breast Cancer: a phase III, randomized, open-label study evaluating the efficacy and safety of giredestrant plus the fixed-dose combination of pertuzumab and trastuzumab for subcutaneous injection in patients with previously untreated HER2-positive, estrogen receptor-positive locally advanced or metastatic breast cancer

BACKGROUND

HER2-positive, estrogen receptor-positive breast cancer (HER2+, ER+ BC) is a distinct disease subtype associated with inferior response to chemotherapy plus HER2-targeted therapy compared with HER2+, ER-negative BC. Bi-directional crosstalk leads to cooperation of the HER2 and ER pathways that may drive treatment resistance; thus, simultaneous co-targeting may optimize treatment impact and survival outcomes in patients with HER2+, ER+ BC. First-line (1L) treatment for patients with HER2+ metastatic BC (mBC) is pertuzumab, trastuzumab, and taxane chemotherapy. In clinical practice, dual HER2 blockade plus a fixed number of chemotherapy cycles are given as induction therapy to maximize tumor response, with subsequent HER2-targeted maintenance treatment given as a more tolerable regimen for long-term disease control. For patients whose tumors co-express ER, maintenance endocrine therapy (ET) can be added, but uptake varies due to lack of data from randomized clinical trials investigating the superiority of maintenance ET plus dual HER2 blockade versus dual HER2 blockade alone. Giredestrant, a novel oral selective ER antagonist and degrader, shows promising clinical activity and manageable safety across phase I-II trials of patients with ER+, HER2-negative BC, with therapeutic potential in those with HER2 co-expression.

METHODS

This phase III, randomized, open-label, two-arm study aims to recruit 812 patients with HER2+, ER+  locally advanced (LA)/mBC into the induction phase (fixed-dose combination of pertuzumab and trastuzumab for subcutaneous injection [PH FDC SC] plus a taxane) to enable 730 patients to be randomized 1:1 to the maintenance phase (giredestrant plus PH FDC SC or PH FDC SC [plus optional ET]), stratified by disease site (visceral versus non-visceral), type of LA/metastatic presentation (de novo versus recurrent), best overall response to induction therapy (partial/complete response versus stable disease), and intent to give ET (yes versus no). The primary endpoint is investigator-assessed progression-free survival. Secondary endpoints include overall survival, objective response rate, clinical benefit rate, duration of response, safety, and patient-reported outcomes.

DISCUSSION

heredERA BC will address whether giredestrant plus dual HER2 blockade is superior to dual HER2 blockade alone, to inform the use of this combination in clinical practice for maintenance 1L treatment of patients with HER2+, ER+ LA/mBC.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT05296798; registered on March 25, 2022. Protocol version 3.0 (November 18, 2022).

SPONSOR

F. Hoffmann-La Roche Ltd, Grenzacherstrasse 124 4070, Basel, Switzerland.

Real-World Data Analysis of CDK4/6 Inhibitor Therapy-A Patient-Centric Single Center Study

BACKGROUND

The quest to comprehend the real-world efficacy of CDK4/6 inhibitors (CDKis) in breast cancer continues, as patient responses vary significantly.

METHODS

This single-center retrospective study evaluated CDKi use outside the trial condition from November 2016 to May 2020. Progression-free survival (PFS), time-to-treatment failure (TTF), short-term and prolonged treatment benefit (≥4 and ≥10 months), as well as prognostic and predictive markers were assessed with Kaplan-Meier and multivariate regression analyses.

RESULTS

Out of 86 identified patients, 58 (67.4%) had treatment failure of which 40 (46.5%) were due to progression. Median PFS and TTF were 12 and 8.5 months, respectively. A total of 57 (66.3%) and 42 (48.8%) patients experienced short-term and prolonged treatment benefit. Independent, significant predictors for PFS were progesterone receptor expression (HR: 0.88), multiple metastatic sites (HR: 2.56), and hepatic metastasis (HR: 2.01). Significant predictors for TTF were PR expression (HR: 0.86), multiple sites (HR: 3.29), adverse events (HR: 2.35), and diabetes (HR: 2.88). Aside from tumor biology and adverse events, treatment modifications like pausing and switching of CDKi were predictive for short-term (OR: 6.73) and prolonged (OR: 14.27) therapeutic benefit, respectively.

CONCLUSIONS

These findings emphasize the importance of tailored treatment strategies, highlighting the role of PR expression, metastatic burden, and therapeutic adjustments in optimizing patient outcomes in real-world breast cancer management.

Hormone Receptor-Positive/HER2-Positive Breast Cancer: Hormone Therapy and Anti-HER2 Treatment: An Update on Treatment Strategies

Hormone receptor (HR)-positive/HER2-positive breast cancer represents a distinct subtype expressing estrogen and progesterone receptors with an overexpression of HER2. Approximately 14% of female breast cancer cases are HER2-positive, with the majority being HR-positive. These tumors show a cross-talk between the hormonal and HER2 pathways; the interaction has implications for the treatment options for the disease. In this review, we analyze the biology of HR-positive/HER2-positive breast cancer and summarize the evidence concerning the standard of care options both in neoadjuvant/adjuvant settings and in advanced disease. Additionally, we focus on new trials and drugs for HR-positive/HER2-positive breast cancer and the new entity: HER2-low breast cancer.

Management of patients with advanced-stage HER2-positive breast cancer: current evidence and future perspectives

Amplification and/or overexpression of ERBB2, the gene encoding HER2, can be found in 15-20% of invasive breast cancers and is associated with an aggressive phenotype and poor clinical outcomes. Relentless research efforts in molecular biology and drug development have led to the implementation of several HER2-targeted therapies, including monoclonal antibodies, tyrosine-kinase inhibitors and antibody-drug conjugates, constituting one of the best examples of bench-to-bedside translation in oncology. Each individual drug class has improved patient outcomes and, importantly, the combinatorial and sequential use of different HER2-targeted therapies has increased cure rates in the early stage disease setting and substantially prolonged survival for patients with advanced-stage disease. In this Review, we describe key steps in the development of the modern paradigm for the treatment of HER2-positive advanced-stage breast cancer, including selecting and sequencing new-generation HER2-targeted therapies, and summarize efficacy and safety outcomes from pivotal studies. We then outline the factors that are currently known to be related to resistance to HER2-targeted therapies, such as HER2 intratumoural heterogeneity, activation of alternative signalling pathways and immune escape mechanisms, as well as potential strategies that might be used in the future to overcome this resistance and further improve patient outcomes.

Unveiling the mechanisms and challenges of cancer drug resistance

Cancer treatment faces many hurdles and resistance is one among them. Anti-cancer treatment strategies are evolving due to innate and acquired resistance capacity, governed by genetic, epigenetic, proteomic, metabolic, or microenvironmental cues that ultimately enable selected cancer cells to survive and progress under unfavorable conditions. Although the mechanism of drug resistance is being widely studied to generate new target-based drugs with better potency than existing ones. However, due to the broader flexibility in acquired drug resistance, advanced therapeutic options with better efficacy need to be explored. Combination therapy is an alternative with a better success rate though the risk of amplified side effects is commonplace. Moreover, recent groundbreaking precision immune therapy is one of the ways to overcome drug resistance and has revolutionized anticancer therapy to a greater extent with the only limitation of being individual-specific and needs further attention. This review will focus on the challenges and strategies opted by cancer cells to withstand the current therapies at the molecular level and also highlights the emerging therapeutic options -like immunological, and stem cell-based options that may prove to have better potential to challenge the existing problem of therapy resistance. Video Abstract.

The CDK4/6 inhibitor revolution - a game-changing era for breast cancer treatment

Cyclin-dependent kinase (CDK) 4/6 inhibition in combination with endocrine therapy is the standard-of-care treatment for patients with advanced-stage hormone receptor-positive, HER2 non-amplified (HR+HER2-) breast cancer. These agents can also be administered as adjuvant therapy to patients with higher-risk early stage disease. Nonetheless, the clinical success of these agents has created several challenges, such as how to address acquired resistance, identifying which patients are most likely to benefit from therapy prior to treatment, and understanding the optimal timing of administration and sequencing of these agents. In this Review, we describe the rationale for targeting CDK4/6 in patients with breast cancer, including a summary of updated clinical evidence and how this should inform clinical practice. We also discuss ongoing research efforts that are attempting to address the various challenges created by the widespread implementation of these agents.

Combining lapatinib and palbociclib inhibits cell proliferation and invasion via AKT signaling pathway in endocrine-resistant breast cancer cells

Endocrine therapy plays a critical role in patients with hormone receptor-positive breast cancer. Endocrine-resistant breast cancer cells exhibit more HER2 signaling proteins (pAKT and pERK) and mesenchymal biomarkers than wild-type cell lines. In head and neck squamous cell carcinoma, the combination of lapatinib and palbociclib demonstrated synergistic inhibitory effects on cell proliferation and suppressed ERK1/2 phosphorylation. The combination of lapatinib and palbociclib at half-maximal inhibitory concentrations resulted in an increasing cytotoxic effect on cell proliferation. Furthermore, invasion activity was significantly decreased when combining two drugs at nontoxic concentrations more than either single drug alone did. The combination also remarkably suppressed epithelial-mesenchymal transition transcription factors, such as Snail and pAKT, more than monotherapy. Combining drugs, particularly lapatinib and palbociclib for targeting endocrine-resistant breast cancer cells whose tumors overexpressed HER2 after resistance to hormonal therapy, demonstrated better antiproliferative, anti-invasive effects, and suppression of EMT protein and pAKT than a single drug. These results could be from the interruption of the EMT process via the AKT pathway. Thus, this study provides preliminary data for applying this combination to patients with endocrine-resistant breast cancer in further clinical trials.

Clinical considerations of CDK4/6 inhibitors in HER2 positive breast cancer

Deregulation of cell cycles can result in a variety of cancers, including breast cancer (BC). In fact, abnormal regulation of cell cycle pathways is often observed in breast cancer, leading to malignant cell proliferation. CDK4/6 inhibitors (CDK4/6i) can block the G1 cell cycle through the cyclin D-cyclin dependent kinase 4/6-inhibitor of CDK4-retinoblastoma (cyclinD-CDK4/6-INK4-RB) pathway, thus blocking the proliferation of invasive cells, showing great therapeutic potential to inhibit the spread of BC. So far, three FDA-approved drugs have been shown to be effective in the management of advanced hormone receptor positive (HR+) BC: palbociclib, abemaciclib, and ribociclib. The combination strategy of CDK4/6i and endocrine therapy (ET) has become the standard therapeutic regimen and is increasingly applied to advanced BC patients. The present study aims to clarify whether CDK4/6i can also achieve a certain therapeutic effect on Human epidermal growth factor receptor 2 positive (HER2+) BC. Studies of CDK4/6i are not limited to patients with estrogen receptor positive/human epidermal growth factor receptor 2 negative (ER+/HER2-) advanced BC, but have also expanded to other types of BC. Several pre-clinical and clinical trials have demonstrated the potential of CDK4/6i in treating HER2+ BC. Therefore, this review summarizes the current knowledge and recent findings on the use of CDK4/6i in this type of BC, and provides ideas for the discovery of new treatment modalities.

Endocrine therapy plus HER2-targeted therapy, another favorable option for HR+/HER2+ advanced breast cancer patients

Advanced breast cancer (ABC) that is positive for hormone receptors (HRs) and human epidermal growth factor receptor 2 (HER2) is a cancer subtype with distinctive characteristics. The primary treatment guidelines suggest that a combination therapy comprising anti-HER2 therapy and chemotherapy should be administered as the initial treatment for HR-positive/ HER2-positive (HR+/HER2+) ABC. However, crosstalk between the HR and HER2 pathways can partially account for the resistance of HR+/HER2+ disease to HER2-targeted therapy. This, in turn, provides a rationale for the concomitant administration of HER2-targeted therapy and endocrine therapy (ET). Many clinical studies have confirmed that the combination of HER2-targeted therapy and ET as a first-line treatment is not inferior to the combination of HER2-targeted therapy and chemotherapy, and support its use as a first-line treatment choice for HR+/HER2+ ABC. Other drugs, such as antibody-drug conjugates, cyclin-dependent kinase 4/6 inhibitors, phosphatidylinositol 3-kinase-protein kinase B (AKT)-mammalian target of rapamycin inhibitors, and programmed cell death protein 1 or programmed cell death ligand 1 inhibitors, may also improve the prognosis of patients with breast cancer by blocking signaling pathways associated with tumor proliferation and break new ground for the treatment of HR+/HER2+ ABC.

Overall Survival and Exploratory Biomarker Analyses of Abemaciclib plus Trastuzumab with or without Fulvestrant versus Trastuzumab plus Chemotherapy in HR+, HER2+ Metastatic Breast Cancer Patients

PURPOSE

The monarcHER trial has shown that abemaciclib, a cyclin-dependent kinase 4 and 6 inhibitor, combined with fulvestrant and trastuzumab, improves progression-free survival (PFS) in hormone receptor-positive (HR+), HER2-positive (HER2+) advanced breast cancer (ABC) compared with standard-of-care (SOC) chemotherapy combined with trastuzumab. We report the final overall survival (OS) analysis, updated safety and efficacy data, and exploratory biomarker results from monarcHER.

PATIENTS AND METHODS

monarcHER (NCT02675231), a randomized, multicenter, open-label, phase II trial, enrolled 237 patients across Arm A (abemaciclib, trastuzumab, fulvestrant), Arm B (abemaciclib, trastuzumab), and Arm C (SOC chemotherapy, trastuzumab). Following the statistical plan, OS and PFS were estimated in all arms. RNA sequencing (RNA-seq) was performed on archival tissue.

RESULTS

Median OS was 31.1 months in Arm A, 29.2 months in Arm B, and 20.7 months in Arm C [A vs. C: HR, 0.71; 95% confidence interval (CI), 0.48-1.05; nominal two-sided P value 0.086; B vs. C: HR 0.83 (95% CI, 0.57-1.23); nominal two-sided P value 0.365]. Updated PFS and safety findings were consistent with previous results. The most frequently reported treatment-emergent adverse events included diarrhea, fatigue, nausea, neutrophil count decrease, and anemia. In exploratory RNA-seq analyses, Luminal subtypes were associated with longer PFS [8.6 vs. 5.4 months (HR, 0.54; 95% CI, 0.38-0.79)] and OS [31.7 vs. 19.7 months (HR, 0.68; 95% CI, 0.46-1.00)] compared with non-Luminal.

CONCLUSIONS

In this phase II trial, abemaciclib + trastuzumab ± fulvestrant numerically improved median OS in women with HR+, HER2+ ABC compared with SOC chemotherapy + trastuzumab.

Safety and Efficacy of Tucatinib, Letrozole, and Palbociclib in Patients with Previously Treated HR+/HER2+ Breast Cancer

PURPOSE

To overcome resistance to antihormonal and HER2-targeted agents mediated by cyclin D1-CDK4/6 complex, we proposed an oral combination of the HER2 inhibitor tucatinib, aromatase inhibitor letrozole, and CDK4/6 inhibitor palbociclib (TLP combination) for treatment of HR+/HER2+ metastatic breast cancer (MBC).

PATIENTS AND METHODS

Phase Ib/II TLP trial (NCT03054363) enrolled patients with HR+/HER2+ MBC treated with ≥2 HER2-targeted agents. The phase Ib primary endpoint was safety of the regimen evaluated by NCI CTCAE version 4.3. The phase II primary endpoint was efficacy by median progression-free survival (mPFS).

RESULTS

Forty-two women ages 22 to 81 years were enrolled. Patients received a median of two lines of therapy in the metastatic setting, 71.4% had visceral disease, 35.7% had CNS disease. The most common treatment-emergent adverse events (AE) of grade ≥3 were neutropenia (64.3%), leukopenia (23.8%), diarrhea (19.0%), and fatigue (14.3%). Tucatinib increased AUC10-19 hours of palbociclib 1.7-fold, requiring palbociclib dose reduction from 125 to 75 mg daily. In 40 response-evaluable patients, mPFS was 8.4 months, with similar mPFS in non-CNS and CNS cohorts (10.0 months vs. 8.2 months; P = 0.9). Overall response rate was 44.5%, median duration of response was 13.9 months, and clinical benefit rate was 70.4%; 60% of patients were on treatment for ≥6 months, 25% for ≥1 year, and 10% for ≥2 years. In the CNS cohort, 26.6% of patients remained on study for ≥1 year.

CONCLUSIONS

TLP combination was safe and tolerable. AEs were expected and manageable with supportive therapy and dose reductions. TLP showed excellent efficacy for an all-oral chemotherapy-free regimen warranting further testing. See related commentary by Huppert and Rugo, p. 4993.

FSIP1 enhances the therapeutic sensitivity to CDK4/6 inhibitors in triple-negative breast cancer patients by activating the Nanog pathway

CDK4/6 inhibitors are routinely recommended agents for the treatment of advanced HR+HER2- breast cancer. However, their therapeutic effectiveness in triple-negative breast cancer (TNBC) remains controversial. Here, we observed that the expression level of fibrous sheath interacting protein 1 (FSIP1) could predict the treatment response of TNBC to CDK4/6 inhibitors. High FSIP1 expression level was related to a poor prognosis in TNBC, which was associated with the ability of FSIP1 to promote tumor cell proliferation. FSIP1 downregulation led to slowed tumor growth and reduced lung metastasis in TNBC. FSIP1 knockout caused cell cycle arrest at the G0/G1 phase and reduced treatment sensitivity to CDK4/6 inhibitors by inactivating the Nanog/CCND1/CDK4/6 pathway. FSIP1 could form a complex with Nanog, protecting it from ubiquitination and degradation, which may facilitate the rapid cell cycle transition from G0/G1 to S phase and exhibit enhanced sensitivity to CDK4/6 inhibitors. Our findings suggest that TNBC patients with high FSIP1 expression levels may be suitable candidates for CDK4/6 inhibitor treatment.

Efficacy of everolimus-based therapy in advanced triple-positive breast cancer: Experience from three cancer centers in China

BACKGROUND

Triple-positive breast cancer (TPBC) is highly invasive and lacks well-established treatment strategies, especially in patients with advanced stage disease. This study aimed to explore the efficacy of everolimus in patients with metastatic TPBC (mTPBC) in a multicenter real-world setting.

METHODS

A total of 2518 cancer patients who received everolimus-based therapy were enrolled from three cancer institutes in China from 2014 to 2022. Their clinicopathological characteristics were collected from medical records. The indicators for the efficacy of everolimus were progression-free survival (PFS), objective response rate (ORR) and clinical benefit rate (CBR).

RESULTS

We collected 79 HER2-enriched patients that were treated with everolimus-based therapy, 43 of whom were mTPBC. The most commonly used therapeutic combinations was everolimus plus endocrine therapy (18/43, 41.9%). Among all combinations, everolimus plus chemotherapy plus trastuzumab developed the longest PFS of 10.9 months (95% CI: 1.5-20.3). Seventeen patients (32.6%) with mTPBC received everolimus as frontline treatment (1 L/2 L/3 L, FL), and 26 patients (67.4%) as backline treatment (>3 L, BL). Among all the population, the median PFS for everolimus was 4.5 months (range: 3.0-6.0), ORR was 30.2%, and CBR was 48.8%. PFSFL of 10.9 months was significantly longer than 4.0 months for PFSBL (p = 0.003, HR = 0.31, 95% CI: 0.14-0.67). ORRFL was 41.2%, showing no significance compared to ORRBL of 23.1% (one-sided p = 0.11). CBRFL was observed better of 76.5% versus CBRBL of 46.2% (one-sided p = 0.026).

CONCLUSION

Everolimus as frontline treatment achieves clinical benefits for Chinese patients with mTPBC, which may provide some references for the management of Chinese mTPBC patients.

The CDK4/6 inhibitors biomarker landscape: The most relevant biomarkers of response or resistance for further research and potential clinical utility

Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6is) in combination with Endocrine Therapy (ET) represent the standard frontline therapy for patients with Hormone Receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic Breast Cancer (mBC). Clinical activity and efficacy of CDK4/6is-based therapies have been proven both in the endocrine sensitive and resistant settings. Therapy resistance eventually underpins clinical progression to any CDK4/6is-based therapies, yet there is a lack of validated molecular biomarkers predictive of either intrinsic or acquired resistance to CDK4/6is in clinical practice. As the "post-CDK4/6is" landscape for the management of HR-positive/HER2-negative mBC is rapidly evolving with the introduction of novel therapies, there is an urgent need for the definition of clinically relevant molecular biomarkers of intrinsic/acquired resistance mechanisms to CDK4/6is. This narrative review outlines the role of currently approved CDK4/6is-based therapies, describes the most relevant molecular biomarkers of CDK4/6is-resistance, and ultimately provides a perspective on the clinical and research scenario.

Differential response of HER2-positive breast cancer to anti-HER2 therapy based on HER2 protein expression level

BACKGROUND

Increasing data indicate that HER2-positive (HER2 + ) breast cancer (BC) subtypes exhibit differential responses to targeted anti-HER2 therapy. This study aims to investigate these differences and the potential underlying molecular mechanisms.

METHODS

A large cohort of BC patients (n = 7390) was utilised. The clinicopathological characteristics and differential gene expression (DGE) of HER2+ immunohistochemical (IHC) subtypes, specifically HER2 IHC 3+ and IHC 2 + /Amplified, were assessed and correlated with pathological complete response (pCR) and survival in the neoadjuvant and adjuvant settings, respectively. The role of oestrogen receptor (ER) status was also investigated.

RESULTS

Compared to HER2 IHC 3+ tumours, BC patients with IHC 2 + /Amplified showed a significantly lower pCR rate (22% versus 57%, P < 0.001), shorter survival regardless of HER2 gene copy number, were less classified as HER2 enriched, and enriched for trastuzumab resistance and ER signalling pathway genes. ER positivity significantly decreased response to anti-HER2 therapy in IHC 2 + /Amplified, but not in IHC 3 + BC patients.

CONCLUSION

In HER2 + BC, overexpression of HER2 protein is the driver of the oncogenic pathway, and it is the main predictor of response to anti-HER2 therapy. ER signalling pathways are more dominant in BC with equivocal HER2 expression. personalised anti-HER2 therapy based on IHC classes should be considered.

HER2-positive breast cancer: cotargeting to overcome treatment resistance

PURPOSE OF REVIEW

The introduction in clinical practice of anti-HER2 agents changed the prognosis of patients with HER2-positive (HER2+) breast cancer in both metastatic and early setting. Although the incomparable results obtained in the last years with the approval of new drugs targeting HER2, not all patients derive benefit from these treatments, experiencing primary or secondary resistance. The aim of this article is to review the data about cotargeting HER2 with different pathways (or epitopes of receptors) involved in its oncogenic signaling, as a mechanism to overcome resistance to anti-HER2 agents.

RECENT FINDINGS

Concordantly to the knowledge of the HER2+ breast cancer heterogeneity as well as new drugs, novel predictive biomarkers of response to anti-HER2 treatments are always raised helping to define target to overcome resistance. Cotargeting HER2 and hormone receptors is the most well known mechanism to improve benefit in HER2+/HR+ breast cancer. Additional HER2-cotargeting, such as, with PI3K pathway, as well as different HERs receptors or immune-checkpoints revealed promising results.

SUMMARY

HER2+ breast cancer is an heterogenous disease. Cotargeting HER2 with other signaling pathways involved in its mechanism of resistance may improve patient outcomes. Research efforts will continue to investigate novel targets and combinations to create more effective treatment regimes.

Dalpiciclib and pyrotinib in women with HER2-positive advanced breast cancer: a single-arm phase II trial

CDK4/6 inhibitors have shown a synergistic effect with anti-HER2 therapy in hormone receptor (HR)-positive and HER2-positive breast cancer (BC). In this phase 2 study (NCT04293276), we aim to evaluate a dual-oral regimen of CDK4/6 inhibitor dalpiciclib combined with HER2 tyrosine kinase inhibitor pyrotinib as front-line treatment in women with HER2-positive advanced BC (n = 41) including those with HR-negative disease. The primary endpoint is the objective response rate, and secondary endpoints include progression-free survival (PFS), overall survival (OS), and safety. With a median follow-up of 25.9 months, 70% (28/40) of assessable patients have a confirmed objective response, meeting the primary endpoint. The median PFS is 11.0 months (95% CI = 7.3-19.3), and OS data are not mature. The most common grade 3 or 4 treatment-related adverse events (AEs) are decreased white blood cell count (68.3%), decreased neutrophil count (65.9%), and diarrhea (22.0%). Most AEs are manageable, and no treatment-related deaths occur. These findings suggest that this combination may have promising activity and manageable toxicity. Further investigation is needed.

MAF1 is a predictive biomarker in HER2 positive breast cancer

RNA polymerase III transcription is pivotal in regulating cellular growth and frequently deregulated in various cancers. MAF1 negatively regulates RNA polymerase III transcription. Currently, it is unclear if MAF1 is universally deregulated in human cancers. Recently, MAF1 expression has been demonstrated to be altered in colorectal and liver carcinomas and Luminal B breast cancers. In this study, we analyzed clinical breast cancer datasets to determine if MAF1 alterations correlate with clinical outcomes in HER2-positive breast cancer. Using various bioinformatics tools, we screened breast cancer datasets for alterations in MAF1 expression. We report that MAF1 is amplified in 39% of all breast cancer sub-types, and the observed amplification co-occurs with MYC. MAF1 amplification correlated with increased methylation of the MAF1 promoter and MAF1 protein expression is significantly decreased in luminal, HER2-positive, and TNBC breast cancer subtypes. MAF1 protein expression is also significantly reduced in stage 2 and 3 breast cancer compared to normal and significantly decreased in all breast cancer patients, regardless of race and age. In SKBR3 and BT474 breast cancer cell lines treated with anti-HER2 therapies, MAF1 mRNA expression is significantly increased. In HER2-positive breast cancer patients, MAF1 expression significantly increases and correlates with five years of relapse-free survival in response to trastuzumab treatment, suggesting MAF1 is a predictive biomarker in breast cancer. These data suggest a role for MAF1 alterations in HER2-positive breast cancer. More extensive studies are warranted to determine if MAF1 serves as a predictive and prognostic biomarker in breast cancer.

Clinical Impact of New Treatment Strategies for HER2-Positive Metastatic Breast Cancer Patients with Resistance to Classical Anti-HER Therapies

HER2-positive breast cancer accounts for 15-20% of all breast cancer cases. This subtype is characterized by an aggressive behavior and poor prognosis. Anti-HER2 therapies have considerably improved the natural course of the disease. Despite this, relapse still occurs in around 20% of patients due to primary or acquired treatment resistance, and metastasis remains an incurable disease. This article reviews the main mechanisms underlying resistance to anti-HER2 treatments, focusing on newer HER2-targeted therapies. The progress in anti-HER2 drugs includes the development of novel antibody-drug conjugates with improvements in the conjugation process and novel linkers and payloads. Moreover, trastuzumab deruxtecan has enhanced the efficacy of trastuzumab emtansine, and the new drug trastuzumab duocarmazine is currently undergoing clinical trials to assess its effect. The combination of anti-HER2 agents with other drugs is also being evaluated. The addition of immunotherapy checkpoint inhibitors shows some benefit in a subset of patients, indicating the need for useful biomarkers to properly stratify patients. Besides, CDK4/6 and tyrosine kinase inhibitors are also included in the design of new treatment strategies. Lapitinib, neratinib and tucatinib have been approved for HER2-positive metastasis patients, however clinical trials are currently ongoing to optimize combined strategies, to reduce toxicity, and to better define the useful setting. Clinical research should be strengthened along with the discovery and validation of new biomarkers, as well as a deeper understanding of drug resistance and action mechanisms.

Metastatic HER2-Positive Breast Cancer: Is There an Optimal Sequence of Therapy?

OPINION STATEMENT

Approximately 20% of breast cancers overexpress human epidermal growth factor receptor 2 (HER2+), conferring a particularly aggressive subtype of the disease with an increased risk for the development of systemic and brain metastases. However, the advent of trastuzumab and more recently several other HER2-targeting novel therapies has led to significant improvements in the prognosis, making the diagnosis a "double-edged sword." The current standard first-line therapy for patients with HER2+ metastatic breast cancer (MBC) is a taxane combined with trastuzumab and pertuzumab. Trastuzumab deruxtecan should be used preferentially in the second line, with the only caveat being patients with CNS involvement where the tucatinib, capecitabine, and trastuzumab regimen could be considered. In the third line setting, given the survival benefits demonstrated with the tucatinib regimen in patients with and without CNS metastases, this is the preferred strategy. In the fourth line and beyond, there is no clear standard. Options include margetuximab in combination with chemotherapy, neratinib + capecitabine, or trastuzumab + chemotherapy. There are several novel therapies under investigation reporting promising results in the late-line setting. The treatment landscape of HER2-positive advanced disease is evolving constantly, with several active therapies being moved to the early-stage setting. Accordingly, it will be critical to identify biomarkers and mechanisms of resistance to optimize therapy selection and maximize patient outcomes and quality of life. Here, we provide an overview of the current and future management of HER2-positive advanced breast cancer and address the specific scenarios which may impact treatment selection including triple-positive breast cancer and the presence of brain metastases. Finally, we highlight promising novel treatments and ongoing trials that may impact future treatment sequencing.

Evolving perspectives on the treatment of HR+/HER2+ metastatic breast cancer

Breast cancer (BC) with expression of the estrogen receptor (ER) and/or progesterone receptor (PR) protein and with overexpression/amplification of the human epidermal growth factor receptor 2 (HER2), termed hormone receptor-positive (HR+)/HER2+ BC, represents ∼10% of all BCs in the United States. HR+/HER2+ BC includes HER2+ BCs that are ER+, PR+, or both ER+ and PR+ (triple-positive BC). Although the current guideline-recommended treatment combination of anti-HER2 monoclonal antibodies plus chemotherapy is an effective first-line therapy for many patients with HER2+ advanced disease, intratumoral heterogeneity within the HR+/HER2+ subtype and differences between the HR+/HER2+ subtype and the HR-/HER2+ subtype suggest that other targeted combinations could be investigated in randomized clinical trials for patients with HR+/HER2+ BC. In addition, published data indicate that crosstalk between HRs and HER2 can lead to treatment resistance. Dual HR and HER2 pathway targeting has been shown to be a rational approach to effective and well-tolerated therapy for patients with tumors driven by HER2 and HR, as it may prevent development of resistance by blocking receptor pathway crosstalk. However, clinical trial data for such approaches are limited. Treatments to attenuate other signaling pathways involved in receptor crosstalk are also under investigation for inclusion in dual receptor targeting regimens. These include cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, based on the rationale that association of CDK4/6 with cyclin D1 may play a role in resistance to HER2-directed therapies, and others such as phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway inhibitors. Herein, we will review the scientific and clinical rationale for combined receptor blockade targeting HER2 and ER for patients with advanced-stage HR+/HER2+ disease.

Emerging Therapies for Breast Cancer

The steady, incremental improvements in outcomes for both early-stage and advanced breast cancer patients are, in large part, attributable to the success of novel systemic therapies. In this review, we discuss key conceptual paradigms that have underpinned this success including (1) targeting the driver: the identification and targeting of major oncoproteins in breast cancers; (2) targeting the lineage pathway: inhibition of those pathways that drive normal mammary epithelial cell proliferation that retain importance in cancer; (3) targeting precisely: the application of molecular classifiers to refine therapy selection for specific cancers, and of antibody-drug conjugates to pinpoint tumor and tumor promoting cells for eradication; and (4) exploiting synthetic lethality: leveraging unique vulnerabilities that cancer-specific molecular alterations induce. We describe promising examples of novel therapies that have been discovered within each of these paradigms and suggest how future drug development efforts might benefit from the continued application of these principles.

CDK4/6 Inhibitor Resistance in Hormone Receptor-Positive Metastatic Breast Cancer: Translational Research, Clinical Trials, and Future Directions

The emergence of CDK4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, has revolutionized the treatment landscape for hormone receptor-positive breast cancer. These agents have demonstrated significant clinical benefits in terms of both progression-free survival and overall survival. However, resistance to CDK4/6 inhibitors remains a challenge, limiting their long-term efficacy. Understanding the complex mechanisms driving resistance is crucial for the development of novel therapeutic strategies and the improvement of patient outcomes. Translational research efforts, such as preclinical models and biomarker studies, offer valuable insight into resistance mechanisms and may guide the identification of novel combination therapies. This review paper aims to outline the reported mechanisms underlying CDK4/6 inhibitor resistance, drawing insights from both clinical data and translational research in order to help direct the future of treatment for hormone receptor-positive metastatic breast cancer.

Thromboembolism profiles associated with cyclin-dependent kinase 4/6 inhibitors: a real-world pharmacovigilance study and a systematic review

BACKGROUND

Thrombosis is the second leading cause of mortality in cancer patients. This study aimed to investigate the association between cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) and thrombosis.

RESEARCH DESIGN AND METHODS

A retrospective pharmacovigilance analysis based on real-world data combined with a systematic review was used to explore the thrombotic risk profiles of CDK4/6i. The study has been registered with Prospero (CRD42021284218).

RESULT

In the pharmacovigilance analysis, CDK4/6i showed a higher rate of reported venous thromboembolism (VTE) (ROR = 2.78, 95% CI = 2.64-2.92), with the highest signal for trilaciclib (ROR = 27.55, 95% CI = 13.43-56.52) but only 9 cases, followed by abemaciclib (ROR = 3.73, 95% CI = 3.19-4.37). For arterial thromboembolism (ATE), only ribociclib increased the reporting rate (ROR = 2.14, 95% CI = 1.91-2.41). In the meta-analysis, palbociclib, abemaciclib, and trilaciclib all increased the risk of VTE (OR = 2.23, 3.17, and 3.90). In the subgroup analysis, only abemaciclib increased the risk of ATE (OR = 2.11, 95% CI = 1.12-3.99)    .

CONCLUSIONS

CDK4/6i had different profiles of thromboembolism. Palbociclib, abemaciclib, or trilaciclib increased the risk of VTE. Ribociclib and abemaciclib showed a weak association with the risk of ATE.

Pyrotinib in combination with letrozole for hormone receptor-positive, human epidermal growth factor receptor 2-positive metastatic breast cancer (PLEHERM): a multicenter, single-arm, phase II trial

BACKGROUND

Human epidermal growth factor receptor 2 (HER2) targeted therapy combined with endocrine therapy has been recommended as an alternative treatment strategy for patients with hormone receptor (HR)-positive, HER2-positive metastatic breast cancer (MBC). This study aimed to evaluate the role of pyrotinib, an oral pan-HER irreversible tyrosine kinase inhibitor, in combination with letrozole for patients with HR-positive, HER2-positive MBC.

METHODS

In this multi-center, phase II trial, HR-positive and HER2-positive MBC patients who were not previously treated for metastasis disease were enrolled. Patients received daily oral pyrotinib 400 mg and letrozole 2.5 mg until disease progression, unacceptable toxicity, or withdrawal of consent. The primary endpoint was the clinical benefit rate (CBR) assessed by an investigator according to the Response Evaluation Criteria in Solid Tumors version 1.1.

RESULTS

From November 2019 to December 2021, 53 patients were enrolled and received pyrotinib plus letrozole. As of August 2022, the median follow-up duration was 11.6 months (95% confidence interval [CI], 8.7-14.0 months). The CBR was 71.7% (95% CI, 57.7-83.2%), and the objective response rate was 64.2% (95% CI, 49.8-76.9%). The median progression-free survival was 13.7 months (95% CI, 10.7-18.7 months). The most common treatment-related adverse event of grade 3 or higher was diarrhea (18.9%). No treatment-related deaths were reported, and one patient experienced treatment discontinuation due to adverse event.

CONCLUSIONS

Our preliminary results suggested that pyrotinib plus letrozole is feasible for the first-line treatment of patients with HR-positive and HER2-positive MBC, with manageable toxicities.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04407988.

Trastuzumab, leuprorelin, letrozole, and palbociclib as first-line therapy in HER2-positive and hormone receptor-positive metastatic breast cancer: A case report

RATIONALE

Cyclin-dependent kinase 4/6 inhibitors are promising candidates for patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer. However, current international guidelines recommend endocrine therapy alone or with HER2-targeted therapy to treat HER2-positive and hormone receptor (HR)-positive metastatic breast cancer in patients who cannot tolerate first-line chemotherapy. Moreover, data on the effectiveness and safety of cyclin-dependent kinase 4/6 inhibitors combined with trastuzumab and endocrine therapy as a first-line treatment for HER2-positive and HR-positive metastatic breast cancer are limited.

PATIENT CONCERNS

A 50-year-old premenopausal woman was with epigastric pain for more than 20 days. Ten years ago, she was diagnosed with left breast cancer and underwent surgical treatment, chemotherapy, and endocrine therapy.

DIAGNOSES

After relevant examination, the patient was diagnosed with liver, lung, and left cervical lymph node metastatic HER2-positive and HR-positive carcinoma from the left breast after systemic therapy.

INTERVENTIONS

The laboratory investigations showed that the patient's liver function was seriously damaged due to the liver metastases, and the patient was assessed as unable to tolerate chemotherapy. She was treated with trastuzumab, leuprorelin, letrozole, and piperacillin combined with percutaneous transhepatic cholangic drainage.

OUTCOMES

The patient's symptoms were relieved, her liver function returned to normal, and the tumor showed partial response. Neutropenia (Grade 3) and thrombocytopenia (Grade 2) occurred during treatment but improved after symptomatic treatment. To date, the progression-free survival of the patient is over 14 months.

LESSONS

We believe that trastuzumab, leuprorelin, letrozole, and palbociclib is a feasible and effective treatment for HER2-positive and HR-positive metastatic breast cancer in premenopausal patients who cannot tolerate first-line chemotherapy.

Estrogen/HER2 receptor crosstalk in breast cancer: combination therapies to improve outcomes for patients with hormone receptor-positive/HER2-positive breast cancer

The human epidermal growth factor receptor 2 (HER2) is overexpressed in 13-22% of breast cancers (BC). Approximately 60-70% of HER2+ BC co-express hormone receptors (HRs). HR/HER2 co-expression modulates response to both anti-HER2-directed and endocrine therapy due to "crosstalk" between the estrogen receptor (ER) and HER2 pathways. Combined HER2/ER blockade may be an effective treatment strategy for patients with HR+/HER2+ BC in the appropriate clinical setting(s). In this review, we provide an overview of crosstalk between the ER and HER2 pathways, summarize data from recently published and ongoing clinical trials, and discuss clinical implications for targeted treatment of HR+/HER2+ BC.

Long-lasting complete remission in a patient with systemic metastases of recurrent breast cancer treated with cyclin-dependent kinases 4/6 inhibitors: a case report

BACKGROUND

The prognosis for recurrence cases of hormone receptor-positive HER2-negative breast cancer remains poor, and treatment strategies that emphasize quality of life have often been chosen, with few physicians aiming for a cure. Our objective is to assess the validity of such current treatment strategies.

CASE PRESENTATION

A 74-year-old Asian woman with multiple lung and liver metastases after local recurrence of breast cancer was treated with two different cyclin-dependent kinases 4/6 inhibitors sequentially in combination with endocrine therapy. Flow cytometric analysis of the patient's peripheral blood mononuclear cells was also performed to evaluate the host's immune status. Complete remission was achieved without cytotoxic agents and the patient remains disease free to this day, 6 years after the initial relapse. Additionally, no increase in the population of the immunosenescent T cells with a phenotype of CD8⁺CD28^- was observed in the patient's peripheral blood mononuclear cells, suggesting that the immune system was well maintained.

CONCLUSIONS

We present this case study to develop new treatment strategies for recurrent breast cancer that is not only bound to misinterpretations of the Hortobagyi algorithm, but also aim for a cure with noncytotoxic agents to maintain the host's immune system and early detection of recurrence.

Identifying the optimal therapeutics for patients with hormone receptor-positive, HER2-positive advanced breast cancer: a systematic review and network meta-analysis

INTRODUCTION

Hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-positive (HER2+) breast cancer is a distinct subtype with different prognosis and response to treatment. HER2-targeted therapy is currently recommended for patients with HR+/HER2+ advanced breast cancer. However, there is debate over which drugs to add on the basis of HER2 blockade yield the optimal efficacy. This systematic review and network meta-analysis was conducted to solve the problem.

METHODS

Eligible randomized controlled trials (RCTs) comparing different interventions in HR+/HER2+ metastatic breast cancer were included. The outcomes of interest included progression-free survival (PFS), overall survival (OS) and treatment-related adverse events (TRAEs). Pooled hazard ratios or odds ratios with credible intervals (CrIs) were calculated to estimate the predefined outcomes. The optimal therapeutics were identified by comparing the surface under the cumulative ranking curves (SUCRA).

RESULTS

Totally, 23 literatures of 20 RCTs were included. Regarding PFS, significant differences were detected between single or dual HER2 blockade plus endocrine therapy (ET) versus ET alone and dual HER2 blockade plus ET versus physician's choice. Trastuzumab, pertuzumab plus chemotherapy significantly improved PFS than trastuzumab plus chemotherapy (hazard ratio 0.69, 95% CrI 0.50-0.92). The SUCRA values suggested the relatively better efficacy of dual HER2-targeted therapy plus ET (86%-91%) than chemotherapy (62%-81%) in prolonging PFS and OS. The HER2 blockade-containing regimens showed similar safety profiles in eight documented TRAEs.

CONCLUSIONS

Prominent status of dual-targeted therapy for patients with HR+/HER2+ metastatic breast cancer was revealed. Compared with chemotherapy-containing regimens, the ET-containing ones showed better efficacy and similar safety profiles, which could be recommended in clinical practice.

A Phase II Single-arm Study of Palbociclib in Patients With HER2-positive Breast Cancer With Brain Metastases and Analysis of ctDNA in Patients With Active Brain Metastases

INTRODUCTION

Palbociclib is highly efficacious and well tolerated in hormone-receptor positive (HR+) metastatic breast cancer (BC) but its activity for HER2+ BC with brain metastases (BM) is unknown.

METHODS

In a single-arm phase II study we evaluated palbociclib with trastuzumab for patients with HER2+ MBC and BM. The primary endpoint was BM response rate. Circulating tumor DNA (ctDNA) was evaluated at baseline, and in a subset of patients at cycle 3 and progression. We also retrospectively identified additional patients with metastatic BC, active BM, and a ctDNA assessment prior to therapy for BM.

RESULTS

Twelve patients with HER2+ MBC were enrolled, 4 with HR+ and 8 with HR- disease. No responses were seen. Best response was stable disease for 6 patients and progressive disease for 6 patients. The median PFS was 2.2 months, interquartile range (IQR) was 1.56 to 3.63 months. The median OS was 13.1 months and IQR was 9.4 to 23.8 months The CNS was the primary site of progression for all patients. The median variant allele fraction (VAF) of the dominant variant in each patient was 0.18% (interquartile range [IQR] 0.12%-0.47%) with a median number of somatic alterations of 1. We additionally evaluated ctDNA results from 26 patients with BC and active BM, among whom the median VAF was 11.8% (IQR 3.9%-27.3%) with a median number of alterations was 6 (IQR 4-9). Notably, progressive systemic disease was significantly less frequent in the trial cohort compared with additional retrospectively identified patients (8% vs. 81%).

CONCLUSION

Palbociclib did not demonstrate activity in HER2+ MBC with BM. Patients with progressive BM but stable, responding, or absent systemic disease have low VAF and number of alterations detected by ctDNA analysis from blood.

Outcomes for the first four lines of therapy in patients with HER2-positive advanced breast cancer: results from the SONABRE registry

PURPOSE

We assessed the systemic treatment choices and outcomes in patients diagnosed with human epidermal growth factor receptor-2-positive (HER2 +) advanced breast cancer (ABC), for the first four lines of systemic therapy and by hormone receptor (HR) status.

METHODS

We identified 330 patients diagnosed with HER2 + ABC in 2013-2018 in the Southeast of The Netherlands, of whom 64% with HR + /HER2 + and 36% with HR-/HER2 + disease. Overall survival (OS) from start of therapy was calculated using the Kaplan-Meier method.

RESULTS

In real world, 95% of patients with HR + /HER2 + and 74% of patients with HR-/HER2 + disease received systemic therapy. In HR + /HER2 + disease, use of endocrine, chemo- and HER2-targeted therapy was , respectively, 64%, 46% and 60% in first line, and 39%, 64% and 75% in fourth line. In HR-/HER2 + disease, 91-96% of patients received chemotherapy and 77-91% HER2-targeted therapy, irrespective of line of therapy. In patients with HR + /HER2 + disease, median OS was 34.9 months (95%CI:25.8-44.0) for the first line and 12.8 months (95%CI:10.7-14.9) for the fourth line. In HR-/HER2 + disease, median OS was 39.9 months (95%CI:23.9-55.8) for the first line and 15.2 months (95%CI:10.9-19.5) for the fourth line. For patients treated with first-line pertuzumab, trastuzumab plus chemotherapy, median OS was not reached at 56.0 months in HR + /HER2 + disease and 48.4 months (95%CI:32.6-64.3) in HR-/HER2 + disease.

CONCLUSION

Survival times for later lines of therapy are surprisingly long and justify the use of multiple lines of systemic therapy in well-selected patients with HER2 + ABC. Our real-world evidence adds valuable observations to the accumulating evidence that within HER2 + ABC, the HR status defines two distinct disease subtypes.

CDK4/6 Inhibitors-Overcoming Endocrine Resistance Is the Standard in Patients with Hormone Receptor-Positive Breast Cancer

PURPOSE OF REVIEW

Tamoxifen and aromatase inhibitors can be considered as some of the first targeted therapies. For the past 30 years, they were the endocrine treatment standard in the advanced and early breast cancer setting. CDK4/6 inhibitors, however, are the first substances in almost two decades to broadly improve the therapeutic landscape of hormone receptor-positive breast cancer patients for the upcoming years. This review is designed to discuss the recent history, current role, future directions and opportunities of this substance class.

RECENT FINDINGS

The CDK4/6 inhibitors abemaciclib, dalpiciclib, palbociclib and ribociclib have all demonstrated a statistically significant improvement in progression-free survival in advanced disease. However, to date, abemaciclib and ribociclib are the only CDK4/6 inhibitors to have shown an improvement in overall survival in patients with metastatic breast cancer. Moreover, abemaciclib is the first CDK4/6 inhibitor to also reduce the risk of recurrence in those with early-stage disease. Further CDK inhibitors, treatment combinations with other drugs and different therapy sequences are in development.

SUMMARY

Achieving significant improvements in survival rates in the advanced and early breast cancer treatment setting, CDK4/6 inhibitors have set a new standard of care for patients with advanced breast cancer. It remains important to better understand resistance mechanisms to be able to develop novel substances and treatment sequences.

Deciphering breast cancer: from biology to the clinic

Breast cancer remains a leading cause of cancer-related mortality in women, reflecting profound disease heterogeneity, metastasis, and therapeutic resistance. Over the last decade, genomic and transcriptomic data have been integrated on an unprecedented scale and revealed distinct cancer subtypes, critical molecular drivers, clonal evolutionary trajectories, and prognostic signatures. Furthermore, multi-dimensional integration of high-resolution single-cell and spatial technologies has highlighted the importance of the entire breast cancer ecosystem and the presence of distinct cellular "neighborhoods." Clinically, a plethora of new targeted therapies has emerged, now being rapidly incorporated into routine care. Resistance to therapy, however, remains a crucial challenge for the field.

Optimizing treatment for HER2-positive HR-positive breast cancer

Triple-positive breast tumors overexpress human epidermal growth factor receptor 2 (HER2) and are positive for hormone receptor (HR) expression. Data from real-life and clinical trials show that estrogen receptor (ER) expression affects the response to combinations of anti-HER2 and associated systemic therapies. Despite triple-positive tumors having decreased response rates compared to HR-negative/HER2-positive breast cancers, optimizing anti-HER2 treatment with dual anti-HER2 blockade remains important for optimal disease control. Preclinical data on the cross-talk between ER and growth factor receptor pathways show the efficacy of combinations of endocrine therapy and anti-HER2 drugs, which is confirmed in the clinic. Molecular dissection of triple-positive breast cancer might provide the rational for additional therapeutic strategies and the identification of promising biomarkers. This review summarizes data on systemic treatment efficacy from major clinical trials and perspectives for future clinical research in triple-positive breast cancer.

[2022: New therapeutic practices in breast oncology]

In women, breast cancer is both the most common and the deadliest. In 2018, an estimated 58,459 new cases were diagnosed in France, and 12,146 patients died. While these figures are impressive, it should be borne in mind that patient survival after treatment for breast cancer has improved significantly and is now 87 % at five years (nearly nine out of ten women), up from 80 % in 1993. This progress is due to the different weapons available to patients and the development of new therapies such as immunotherapy or drug-conjugated antibodies. The classification of breast cancers is also evolving, in particular through the identification of biomarkers that enable the therapeutic strategy to be refined (PD-L1, BRCA…). New anti-HER2 molecules, such trastuzumab deruxtecan, have shown very promising therapeutic activity in patients with breast cancer with low HER2 expression. The search for the BRCA constitutional mutation helps to optimise management. The use of pembrolizumab in the metastatic setting is now possible in tumours expressing PD-L1 with a threshold expression of the PD-L1marker of CPS ≥ 10. In addition, late 2021/early 2022 has provided evidence that collaboration between physicians and patient networks facilitates better access to treatment. This review presents advances in adjuvant and metastatic breast cancer presented at ASCO and ESMO in 2022.

Systemic Therapy for Early- and Late-Stage, Human Epidermal Growth Factor Receptor-2-Positive Breast Cancer

Systemic therapy for both early-stage and metastatic human epidermal growth factor receptor-2-positive (HER2+) breast cancer has seen significant evolution over the last 20 or more years. Innovative trials leveraging the prognostic and predictive information that neoadjuvant chemotherapy provides has led to preoperative systemic therapy becoming the overwhelmingly favored sequencing in the early-stage setting. However, deintensification of therapy is important to consider for patients with good-risk disease or significant comorbidities. Finally, with the abundance of newly approved agents, drug sequencing in the second-line setting has become an important and individualized decision for patients with metastatic disease.

Twelve ESMO Congress 2022 breakthroughs: practicing oncologists' perceptions and potential application on presented data

BACKGROUND

During the European Society for Medical Oncology (ESMO) Congress 2022, outcome data of a great number of clinical trials were presented. For the attending medical oncologist, it is important to structure these data in a way that facilitates a trade-off between treatment burden and benefit.

MATERIALS AND METHODS

To illustrate this, we carried out a narrative non-systematic review of 12 selected oral presentations with potential impact on future daily practice, focusing on trial methodology, possible study flaws, reported clinical benefit and implementability.

RESULTS

The selected presentations encompassed 10 phase III trials, 1 randomized phase II trial and 1 phase II trial. In 7 out of 12 trials, quality of life and/or patient-reported outcomes had been evaluated. None of the trials, which reported progression-free survival (PFS) data, provided information, which could exclude informative censoring bias. In none of the trials reporting overall survival (OS) data, potential flaws due to undesirable crossover and imbalance between study groups regarding post-progression treatments were addressed. For the 11 reviewed randomized trials, the ESMO-Magnitude of Clinical Benefit Scale (MCBS) grade achieved with the new intervention was calculated based on the presented data. The MCBS grade varied from 1 to 5.

CONCLUSIONS

Our review confirms the high-quality standard of current cancer research and the clinical relevance of the research questions answered. However, during presentation of PFS and/or OS data, factors known to affect PFS and OS analysis should be structurally addressed. In order to keep cancer care affordable and sustainable, it could be considered to include an ESMO-MCBS threshold in the drug appraisal process of regulatory authorities.

New treatment strategies for human epidermal growth factor receptor 2-positive breast cancer in 2023

PURPOSE OF REVIEW

Taxanes in combination with trastuzumab and pertuzumab are the established first-line standard in the treatment of human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer. In the last years, several new HER2-targeted therapies, including antibody-drug conjugates (ADCs) and tyrosine kinase inhibitors, have been approved for therapy after trastuzumab or dual blockade. In this review, the current treatment algorithms are discussed, including these new treatment options.

RECENT FINDINGS

The ADC T-DM1 was the established second-line standard based on the results of the EMILIA trial. Recently, the DESTINY-Breast03 trial compared T-DM1 with the new ADC trastuzumab deruxtecan (T-DXd) in patients with disease progression after treatment with taxanes and trastuzumab. T-DXd was associated with an improved progression-free survival and a trend toward improved overall survival, establishing T-DXd as a new second-line standard. The HER2CLIMB trial demonstrated a significant progression-free survival and overall survival benefit for the tyrosine kinase inhibitor tucatinib in combination with trastuzumab and capecitabine after T-DM1 and trastuzumab/pertuzumab. This benefit was also observed in patients with active brain metastases defining this combination as the preferred second or third-line option in these patients.

SUMMARY

New treatment strategies in HER2-positive metastatic breast cancer have substantially improved the clinical outcome of these patients, including those with active brain metastases.

Innovative Therapeutic Approaches for Patients with HER2-Positive Breast Cancer

Overexpression of human epidermal growth factor receptor 2 (HER2), a transmembrane tyrosine kinase receptor, has been described in about 15-20% of breast cancer (BC) and is associated with poor outcomes. Trastuzumab is the first anti-HER2 monoclonal antibody (mAB) that blocks receptor activity but it also activates immune response against cancer cells, thus, revolutionizing the prognosis of patients with HER2-positive BC. Over the years, new therapies have been developed, including other mAbs and tyrosine kinase inhibitors (TKIs) that required multimodal approaches with chemotherapy to optimize their anticancer activity. This chapter gives a comprehensive overview of the last advancements including new approaches and future combinations, which seem to be very promising in overcoming resistance to the traditional anti-HER2 treatments. A modern therapeutic algorithm should include treatment options based on tumour patterns and a patient-centred approach. A proper patient's selection is crucial to derive maximal benefits from a treatment strategy and emerging biomarkers should be integrated along with the HER2 status, which is currently the only validated biomarker in the context of HER2-positive disease. These biomarkers might include molecular features with reported prognostic/predictive significance, such as phosphatidylinositol 3' -kinase (PI3K) or mitogen-activated protein kinase (MAPK) pathways, programmed cell death protein ligand 1 (PD-L1), and tumour-infiltrating lymphocytes (TILs), which all affect prognosis and response to treatments.

Targeting HER2-positive breast cancer: advances and future directions

The long-sought discovery of HER2 as an actionable and highly sensitive therapeutic target was a major breakthrough for the treatment of highly aggressive HER2-positive breast cancer, leading to approval of the first HER2-targeted drug - the monoclonal antibody trastuzumab - almost 25 years ago. Since then, progress has been swift and the impressive clinical activity across multiple trials with monoclonal antibodies, tyrosine kinase inhibitors and antibody-drug conjugates that target HER2 has spawned extensive efforts to develop newer platforms and more targeted therapies. This Review discusses the current standards of care for HER2-positive breast cancer, mechanisms of resistance to HER2-targeted therapy and new therapeutic approaches and agents, including strategies to harness the immune system.

Pigment epithelium-derived factor downregulation in oestrogen receptor positive breast cancer bone metastases is associated with menopause

Pigment epithelium-derived factor (PEDF) has a critical role in bone development and anti-tumour function in breast cancer (BC). As the expression and role of PEDF in BC bone metastases is unknown, we aimed to characterise PEDF in primary and metastatic BC. Subcellular PEDF localisation was semi-quantitatively analysed via immunohistochemistry in patient-matched, archived formalin-fixed paraffin-embedded primary BC and liver, lung, and decalcified bone metastases specimens. PEDF localisation was evaluated in 23 metastatic BC patients diagnosed with ER+, human epidermal growth factor receptor-2 (HER2) negative BC or TNBC. Cytoplasmic (p = 0.019) and membrane (p = 0.048) PEDF was lower in bone metastases compared to primary ER+/HER2- BC. In contrast, nuclear PEDF scores were higher in metastases compared to primary TNBC (p = 0.027), and increased membrane PEDF in metastatic tissue had improved disease-free interval (p = 0.016). Nuclear PEDF was decreased in bone metastases compared to primary ER+//HER2- BC in post-menopausal patients (p = 0.029). These novel findings indicate PEDF plays a role in clinical BC metastasis. Significantly lower PEDF levels in the post-menopausal compared to pre-menopausal setting suggests future PEDF research may have greater clinical importance in the post-menopausal ER+/HER2- BC population.

Treatment strategies for hormone receptor-positive, human epidermal growth factor receptor 2-positive (HR+/HER2+) metastatic breast cancer: A review

Hormone receptor-positive HER2-positive (HR+/HER2+) metastatic breast cancer (MBC) is a unique subtype of breast cancer. Most current guidelines recommend that combination regimens based on anti-HER2 therapy should be used as first-line treatment for HER2+ MBC, irrespective of HR status. Endocrine therapy can be applied as maintenance therapy for patients who are intolerant to chemotherapy or post-chemotherapy. Increasing evidence suggests that complex molecular crosstalk between HR and HER2 pathways may affect the sensitivity to both HER2-targeted and endocrine therapy in patients with HR+/HER2+ breast cancer. Recent research and clinical trials have revealed that a combination of endocrine therapy and anti-HER2 approaches without chemotherapy provides along-term disease control for some patients, but the challenge lies in how to accurately identify the subsets of patients who can benefit from such a de-chemotherapy treatment strategy. In this review, we aim to summarize the results of preclinical and clinical studies in HR+/HER2+ MBC and discuss the possibility of sparing chemotherapy in this subgroup of patients.